Help with Martin Logan Aerius Speakers

Hello all...

My listening room is very well dimensioned... I'd say about 15 feet wide, 23 feet long, and 14 feet high. My ML Aerius's are about 3 feet from the back wall, and about 3.75 feet from the side walls. They are about 7.5 feet apart from each other, toed in about 1.5-2 inches toward the listening position (which is about 10 feet away).
Everything sounds great, imaging is very precise, and I'm pretty happy with the soundstage. My only (albeit slight) complaint is the bass... a little on the boomy, muddy side. I'm looking to "clean" up the bass a little, but I have a few questions...

(1) Is this just a weak point with the ML Aerius speakers?
(2) I opened up the back panel... will adding more "stuffing" tighten up the bass? I'm not too concerned with extension down in to the low 30hz region... more interested in a cleaner, tighter bass.
(3) Would adding vibration damping materials to the woofer enclosure help?

I've tried some feable attempts at room treatments (couch pillows and such placed in the corners), and it didn't help very much. Also, I've tried all sorts of different placements in the room... What I have right now is the best for imaging and soundstage, and, like I said, the bass issue is not THAT big a deal. BUT, I figured I might ask for some input... Thanks in advance!